The subject matter disclosed herein relates generally to imaging systems, and more particularly to an apparatus and method for motion-correcting medical images.
Multi-modality imaging systems exist that scan using different modalities, for example, Computed Tomography (CT), Magnetic Resonance Imaging (MRI), Positron Emission Tomography (PET), and Single Photon Emission Computed Tomography (SPECT). During operation, the image quality of the conventional imaging systems may be affected by the motion of the object being imaged. In particular, motion of the imaged object can degrade the image quality. More specifically, image artifacts are produced by movement of the object during image acquisition. Respiratory motion is a common source of involuntary motion in mammals (e.g., people and animals) encountered in medical imaging systems. The respiratory motion may lead to errors during image review, such as when a physician is determining the size of a lesion, determining the location of the lesion, or quantifying the lesion.
Moreover, in multi-modality systems, for example, an integrated PET/CT system, the PET and CT images should be registered with one another. However, since the CT images are typically acquired during a short time period, the attenuation map generated by the CT images represents the attenuation characteristics of the patient during full exhalation where there is no breathing motion. In contrast, the PET images are typically acquired over a relatively long time period where a patient is allowed to breathe freely due to the long acquisition time. The mismatch between the two data acquisition modes may result in image artifacts in the attenuation corrected PET images.
One known method for reducing the imaging artifacts is to average the CT image (or the maximum intensity CT image) of multiple respiratory phases to mimic the effect of the PET acquisition collected over multiple respiratory cycles. Another known method for reducing the imaging artifacts is to use respiratory gated CT acquisitions to generate attenuation correction maps that better match the respiratory characteristics of the respiratory gated PET acquisition. A further method may include requesting the patient to hold his breath during the scan. However, because PET data may be acquired over several minutes, the patient typically has to breath several times during the PET acquisition, resulting in image artifacts